As Kitty begins to unravel due to the imminent threat to her safety, Sherlock and Joan intensify their efforts to help her. Also, the origin of Sherlock and Kitty's relationship is revealed.
The duo goes against a clever opponent, who forces Holmes to think out of the box. Meanwhile Watson's troubles with her father are brought into focus when he writes a book about her and Holmes.
While recovering from his gun shot wounds, Holmes eschews painkillers while working on a case of a Greek shipping magnate - involving an assassination and currency manipulation - before his final showdown with Moriarty.
Sherlock is called in on a case and immediately recognizes the work of an old foe from Britain. Sherlock sees it as a chance at redemption in catching the man, but first he needs to control his own emotions about the murderer.
Holmes reconnects with Irene, his one true love that he thought had been taken from him by Moriarity. He tries to protect her as she recovers from her trauma but he soon learns that it isn't she that needs protection.
Moriarty asks Holmes to find out who murdered a mechanic in Brooklyn. Despite Watson's protests, Holmes thinks this case will help him uncover Moriarty's true identity, but it will, in fact, lead Holmes to something much worse.
In the series' finale, Holmes and Watson battle with tech billionaire Odin Reichenbach and receive word of their old enemy and Sherlock's former love, Jamie Moriarty.
